This invention relates to the field of communications, and in particular to a method and system for managing a wireless network wherein wireless devices are free to roam among multiple Basic Service Sets (BSSs) in an Extended Service Set (ESS).
Mobile devices, such as laptop computers, personal data assistants (PDAs), headsets, voice over IP (VOIP) phones, and so on, are becoming increasingly popular, and standards and protocols, such as IEEE 802.11 and Bluetooth have been established to facilitate the networking of such devices to form wireless local area networks (WLANs).
Conventionally, the mobile device establishes a connection via an access point (AP) on the WLAN and monitors the quality of the connection. When the quality of the connection becomes marginal, such as occurs when the mobile device travels away from the access point, the mobile device searches for another access point in the network having potentially better quality. Upon detection of another access point with better quality, the mobile device establishes communication with this other access point and cancels the connection with the prior access point. The other access point may be in the same sub-network, or Basic Service Set (BSS), as the original access point, or in a different sub-network that is coupled to the original sub-network, forming an Extended Service Set (ESS).
The continued monitoring of signal quality, and searching for alternative access points by the mobile device consumes power that could otherwise be used for the communication of information over the network. U.S. patent application “METHOD AND SYSTEM FOR ENABLING CENTRALIZED CONTROL OF WIRELESS LOCAL AREA NETWORKS”, publication number 2002/0085719, filed 22 Oct. 2001 for David B. Crosbie, incorporated by reference herein, discloses the use of a roaming server that monitors the quality of the links between access points and wireless devices, and effects a substantially seamless transfer of the wireless devices to alternative access points as required. The transfer of a wireless device to an alternative access point may also be triggered based on the congestion of particular links, the location of the wireless device, or an explicit request from either the access point or the mobile device. The seamless transfer is achieved by “address-spoofing”. The roaming server transfers the “session data” from the original access point to the new access point, so that the new access point adopts the address of the original access point, along with other communications parameters, such as the frequency offset, hop sequence, encryption key, and so on. To assure continuous communication, the clocks are synchronized by having the wireless device assume a ‘master’ role with the original access point, then assume a ‘slave’ role with the new access point. Although this scheme provides a seamless transfer of the wireless device from the original access point to the new access point, this session-data spoofing and master-then-slave clock synchronization is contrary to the underlying autonomous principles of conventional networking protocols.